Polycrystalline diamond partially depleted of catalyzing material

ABSTRACT

The present invention provides a method of making an earth boring drill bit having a superhard polycrystalline diamond or diamond-like element with greatly improved resistance to thermal degradation without loss of impact strength. Collectively called PCD elements, these elements are formed with a binder-catalyzing material in a high-temperature, high-pressure process. The PCD element has a plurality of partially bonded diamond or diamond-like crystals forming at least one continuous diamond matrix, and the interstices among the diamond crystals forming at least one continuous interstitial matrix containing a catalyzing material. The element has a working surface and a body, where a portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/682,042 filed on Jul. 13, 2001, now U.S. Pat. No. 6,592,985 by NigelD. Griffin and Peter R. Hughes, hereby incorporated by reference herein,which claims priority from U.S. Provisional Patent Application No.60/234,075 filed Sep. 20, 2000, and from U.S. Provisional PatentApplication No. 60/281,054 filed Apr. 2, 2001.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to superhard polycrystalline material elements forwear, cutting, drawing, and other applications where engineeredsuperhard surfaces are needed. The invention particularly relates topolycrystalline diamond and polycrystalline diamond-like (collectivelycalled PCD) elements with greatly improved wear resistance and methodsof manufacturing them.

2. Description of Related Art

Polycrystalline diamond and polycrystalline diamond-like elements areknown, for the purposes of this specification, as PCD elements. PCDelements are formed from carbon based materials with exceptionally shortinter-atomic distances between neighboring atoms. One type ofpolycrystalline diamond-like material is known as carbonitride (CN)described in U.S. Pat. No. 5,776,615. Another, more commonly used formof PCD is described in more detail below. In general, PCD elements areformed from a mix of materials processed under high-temperature andhigh-pressure into a polycrystalline matrix of inter-bonded superhardcarbon based crystals. A common trait of PCD elements is the use ofcatalyzing materials during their formation, the residue from which,often imposes a limit upon the maximum useful operating temperature ofthe element while in service.

A well known, manufactured form of PCD element is a two-layer ormulti-layer PCD element where a facing table of polycrystalline diamondis integrally bonded to a substrate of less hard material, such astungsten carbide. The PCD element may be in the form of a circular orpart-circular tablet, or may be formed into other shapes, suitable forapplications such as hollow dies, heat sinks, friction bearings, valvesurfaces, indentors, tool mandrels, etc. PCD elements of this type maybe used in almost any application where a hard wear and erosionresistant material is required. The substrate of the PCD element may bebrazed to a carrier, often also of cemented tungsten carbide. This is acommon configuration for PCD“s used as cutting elements, for example infixed cutter or rolling cutter earth boring bits when received in asocket of the drill bit, or when fixed to a post in a machine tool formachining. These PCD elements are typically called PDC“s.

Another form of PCD element is a unitary PCD element without an integralsubstrate where a table of polycrystalline diamond is fixed to a tool orwear surface by mechanical means or a bonding process. These PCDelements differ from those above in that diamond particles are presentthroughout the element. These PCD elements may be held in placemechanically, they may be embedded within a larger PCD element that hasa substrate, or, alternately, they may be fabricated with a metalliclayer which may be bonded with a brazing or welding process. A pluralityof these elements may be made from a single PCD, as shown, for example,in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporated byreference for all they disclose.

PCD elements are most often formed by sintering diamond powder with asuitable binder-catalyzing material in a high-pressure, high-temperaturepress. One particular method of forming this polycrystalline diamond isdisclosed in U.S. Pat. No. 3,141,746 herein incorporated by referencefor all it discloses. In one common process for manufacturing PCDelements, diamond powder is applied to the surface of a preformedtungsten carbide substrate incorporating cobalt. The assembly is thensubjected to very high temperature and pressure in a press. During thisprocess, cobalt migrates from the substrate into the diamond layer andacts as a binder-catalyzing material, causing the diamond particles tobond to one another with diamond-to-diamond bonding, and also causingthe diamond layer to bond to the substrate.

The completed PCD element has at least one matrix of diamond crystalsbonded to each other with many interstices containing abinder-catalyzing material metal as described above. The diamondcrystals comprise a first continuous matrix of diamond, and theinterstices form a second continuous matrix of interstices containingthe binder-catalyzing material. In addition, there are necessarily arelatively few areas where the diamond to diamond growth hasencapsulated some of the binder-catalyzing material. These “islands” arenot part of the continuous interstitial matrix of binder-catalyzingmaterial.

In one common form, the diamond element constitutes 85% to 95% by volumeand the binder-catalyzing material the other 5% to 15%. Such an elementmay be subject to thermal degradation due to differential thermalexpansion between the interstitial cobalt binder-catalyzing material anddiamond matrix beginning at temperatures of about 400 degrees C. Uponsufficient expansion the diamond-to-diamond bonding may be ruptured andcracks and chips may occur.

Also in polycrystalline diamond, the presence of the binder-catalyzingmaterial in the interstitial regions adhering to the diamond crystals ofthe diamond matrix leads to another form of thermal degradation. Due tothe presence of the binder-catalyzing material, the diamond is caused tographitize as temperature increases, typically limiting the operationtemperature to about 750 degrees C.

Although cobalt is most commonly used as the binder-catalyzing material,any group VIII element, including cobalt, nickel, iron, and alloysthereof, may be employed.

To reduce thermal degradation, so-called “thermally stable”polycrystalline diamond components have been produced as preform PCDelements for cutting and/or wear resistant elements, as disclosed inU.S. Pat. No. 4,224,380 herein incorporated by reference for all itdiscloses. In one type of thermally stable PCD element the cobalt orother binder-catalyzing material in conventional polycrystalline diamondis leached out from the continuous interstitial matrix after formation.While this may increase the temperature resistance of the diamond toabout 1200 degrees C., the leaching process also removes the cementedcarbide substrate. In addition, because there is no integral substrateor other bondable surface, there are severe difficulties in mountingsuch material for use in operation.

The fabrication methods for this “thermally stable” PCD elementtypically produce relatively low diamond densities, of the order of 80%or less. This low diamond density enables a thorough leaching process,but the resulting finished part is typically relatively weak in impactstrength.

In an alternative form of thermally stable polycrystalline diamond,silicon is used as the catalyzing material. The process for makingpolycrystalline diamond with a silicon catalyzing material is quitesimilar to that described above, except that at synthesis temperaturesand pressures, most of the silicon is reacted to form silicon carbide,which is not an effective catalyzing material. The thermal resistance issomewhat improved, but thermal degradation still occurs due to someresidual silicon remaining, generally uniformly distributed in theinterstices of the interstitial matrix. Again, there are mountingproblems with this type of PCD element because there is no bondablesurface.

More recently, a further type of PCD has become available in whichcarbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba are used asthe binder-catalyzing material when sintering the diamond powder. PCD ofthis type typically has greater wear-resistance and hardness than theprevious types of PCD elements. However, the material is difficult toproduce on a commercial scale since much higher pressures are requiredfor sintering than is the case with conventional and thermally stablepolycrystalline diamond. One result of this is that the bodies ofpolycrystalline diamond produced by this method are smaller thanconventional polycrystalline diamond elements. Again, thermaldegradation may still occur due to the residual binder-catalyzingmaterial remaining in the interstices. Again, because there is nointegral substrate or other bondable surface, there are difficulties inmounting this material to a working surface.

Efforts to combine thermally stable PCD“s with mounting systems to puttheir improved temperature stability to use have not been as successfulas hoped due to their low impact strength. For example, various ways ofmounting multiple PCD elements are shown in U.S. Pat. Nos. 4,726,718;5,199,832; 5,025,684; 5,238,074; 6,009,963 herein incorporated byreference for all they disclose. Although many of these designs have hadcommercial success, the designs have not been particularly successful incombining high wear and/or abrasion resistance while maintaining thelevel of toughness attainable in non-thermally stable PCD.

Other types of diamond or diamond like coatings for surfaces aredisclosed in U.S. Pat. Nos. 4,976,324; 5,213,248; 5,337,844; 5,379,853;5,496,638; 5,523,121; 5,624,068 all herein incorporated by reference forall they disclose. Similar coatings are also disclosed in GB PatentPublication No. 2,268,768, PCT Publication No. 96/34,131, and EPCPublications 500,253; 787,820; 860,515 for highly loaded tool surfaces.In these publications, diamond and/or diamond like coatings are shownapplied on surfaces for wear and/or erosion resistance.

In many of the above applications physical vapor deposition (PVD) and/orvapor deposition (CVD) processes are used to apply the diamond ordiamond like coating. PVD and CVD diamond coating processes are wellknown and are described for example in U.S. Pat. Nos. 5,439,492;4,707,384; 4,645,977; 4,504,519; 4,486,286 all herein incorporated byreference.

PVD and/or CVD processes to coat surfaces with diamond or diamond likecoatings may be used, for example, to provide a closely packed set ofepitaxially oriented crystals of diamond or other superhard crystals ona surface. Although these materials have very high diamond densitiesbecause they are so closely packed, there is no significant amount ofdiamond to diamond bonding between adjacent crystals, making them quiteweak overall, and subject to fracture when high shear loads are applied.The result is that although these coatings have very high diamonddensities, they tend to be mechanically weak, causing very poor impacttoughness and abrasion resistance when used in highly loadedapplications such as with cutting elements, bearing devices, wearelements, and dies.

Some attempts have been made to improve the toughness and wearresistance of these diamond or diamond like coatings by application to atungsten carbide substrate and subsequently processing in ahigh-pressure, high-temperature environment as described in U.S. Pat.Nos. 5,264,283; 5,496,638; 5,624,068 herein incorporated by referencefor all they contain. Although this type of processing may improve thewear resistance of the diamond layer, the abrupt transition between thehigh-density diamond layer and the substrate make the diamond layersusceptible to wholesale fracture at the interface at very low strains.This translates to very poor toughness and impact resistance in service.

When PCD elements made with a cobalt or other group VIII metalbinder-catalyzing material were used against each other as bearingmaterials, it was found that the coefficient of friction tended toincrease with use. As described in European Patent specification number617,207, it was found that removal (by use of a hydrochloric acid wipe)of the cobalt-rich tribofilm which tended to build up in service fromthe surface of the PCD bearing element, tended to mitigate this problem.Apparently, during operation, some of the cobalt from the PCD at thesurface migrates to the load area of the bearing, causing increasedfriction when two PCD elements act against each other as bearings. It isnow believed that the source of this cobalt may be a residual by-productof the finishing process of the bearing elements, as the acid wiperemedy cannot effectively remove the cobalt to any significant depthbelow the surface.

Because the cobalt is removed only from the surface of the PCD, there isno effective change in the temperatures at which thermal degradationoccurs in these bearing elements. Therefore the deleterious effects ofthe binder-catalyzing material remain, and thermal degradation of thediamond layer due to the presence of the catalyzing material stilloccurs.

SUMMARY OF THE INVENTION

The present invention provides a superhard polycrystalline diamond ordiamond-like element with greatly improved resistance to thermaldegradation without loss of impact strength. Collectively called PCDelements for the purposes of this specification, these elements areformed with a binder-catalyzing material in a high-temperature,high-pressure process. The PCD element has a plurality of partiallybonded diamond or diamond-like crystals forming at least one continuousdiamond matrix, and the interstices among the diamond crystals formingat least one continuous interstitial matrix containing a catalyzingmaterial. The element has a working surface and a body, where a portionof the interstitial matrix in the body adjacent to the working surfaceis substantially free of the catalyzing material, and the remaininginterstitial matrix contains the catalyzing material.

A portion of the working surface on the body of the PCD element may bepost-processed so that the interstices among the superhard crystals aresubstantially free of the catalyzing material. The working surface thatis substantially free of the catalyzing material is not subject to thethermal degradation encountered in the other areas of the workingsurface, resulting in improved resistance to thermal degradation. Incutting elements, the processed working surface may be a portion of thefacing table of the body, a portion of the peripheral surface of thebody, or portions of all these surfaces.

In another embodiment, the catalyzing material is cobalt or other irongroup metal, and the method of depleting the catalyzing material is toleach it from the interstices near the surface of a PCD element in anacid etching process. It is anticipated that the method of removing thecatalyzing material from the surface may also be by electricaldischarge, or other electrical or galvanic process, or by evaporation.

In another embodiment, the catalyzing material is subsequently removedfrom the working surface of a PCD element by combining it chemicallywith another material such that it no longer acts as a catalyzingmaterial. In this method, a material may remain in the interstices amongthe diamond crystals, but that material no longer acts as a catalyzingmaterial effectively removing or depleting the catalyzing material.

In still another embodiment, the catalyzing material is removed bycausing it to transform into a material that no longer acts as acatalyzing material. This may be accomplished by a crystal structurechange, mechanical “working”, thermal treatment or other treatmentmethods. This method may apply to non-metallic or non-reactivecatalyzing materials. Again, a material may remain in the intersticesamong the superhard material crystals, but that material no longer actsas a catalyzing material effectively removing or depleting thecatalyzing material.

Disclosed is an element comprising a plurality of partially bondeddiamond crystals, a catalyzing material, an interstitial matrix, and abody with a working surface. The interstitial matrix in the bodyadjacent to the working surface is substantially free of the catalyzingmaterial, and the remaining interstitial matrix contains the catalyzingmaterial.

Similarly, a PCD element is disclosed having a catalyzing material, aninterstitial matrix, and a body with a working surface. The interstitialmatrix in the body adjacent to the working surface is substantially freeof the catalyzing material, and the remaining interstitial matrixcontains the catalyzing material.

Also, a PCD element is disclosed having a plurality of superhardcrystals, a catalyzing material and a body with a working surface. Inthis element, a majority of the crystals in the body within at least a0.1 mm depth from the working surface have a surface which issubstantially free of the catalyzing material and the remaining crystalsare contacting the catalyzing material.

Furthermore, a PCD element is disclosed having a body with a workingsurface. A first volume of the body remote from the working surfacecontains a catalyzing material, and a second volume of the body adjacentto the working surface is substantially free of the catalyzing material.

Also, an element is disclosed having a plurality of partially bondeddiamond crystals, a catalyzing material, and a body with a workingsurface. The volume of the body adjacent the working surface has asubstantially higher diamond density than elsewhere in the body, and thevolume is substantially free of the catalyzing material.

Also, a PCD element is disclosed having a body with a working surface.The volume of the body adjacent to the working surface has a diamonddensity substantially higher than elsewhere in the body, and the volumeis substantially free of a catalyzing material.

In addition, a preform cutting element is disclosed. The element has afacing table of a superhard polycrystalline material having a pluralityof partially bonded superhard crystals, a plurality of interstitialregions among the superhard crystals and a catalyzing material. Thefacing table has a cutting surface and a body. The interstitial regionsin at least a portion of the cutting surface are substantially free ofthe catalyzing material and the remainder of the interstitial regionscontain the catalyzing material.

The PCD elements of the present invention may be used for wear, cutting,drawing, and other applications where engineered diamond surfaces areneeded. Specific applications are as cutting elements in rotary drillbits of both the fixed cutter type and the rolling cutter type, ashollow dies, heat sinks, friction bearings, valve surfaces, indentors,tool mandrels, etc. The PCD element of the present invention may be usedto machine abrasive wood products, ferrous and nonferrous materials andalso very hard or abrasive engineering materials such as stone andasphalt and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a typical PCD element of the present invention.

FIG. 1B is a typical PCD of the present invention shown as a cuttingelement.

FIG. 2 is a side view of a fixed cutter rotary drill bit using a PCDelement of the present invention.

FIG. 3 is a perspective view of a rolling cutter rotary drill bit usinga PCD element of the present invention.

FIG. 4 is a perspective view of an insert used in machine toolsutilizing the PCD element of the present invention.

FIG. 5 is a perspective view of a dome shaped PCD element suitable foruse in both rolling cutter drill bits and in fixed cutter drill bits.

FIG. 6 is a photo-micrograph of the surface of a PCD element of theprior art showing the binder-catalyzing material in the interstitialregions.

FIG. 7 is a photo-micrograph of the PCD element of the present inventionshowing a first portion with a catalyzing material in the interstitialregions and a second portion without the catalyzing material in theinterstitial regions.

FIG. 8 is a micro-structural representation of a PCD element of theprior art, showing the bonded diamond crystals, with the interstitialregions and the crystallographic orientation of the individual crystals.

FIG. 9 is a micro-structural representation of the PCD element of thepresent invention as shown in FIG. 7, indicating the depth of thecatalyzing material free region relative to the surface of the PCDelement.

FIG. 10 is a graph of the relative wear indices of several embodimentsof the PCD element of the present invention.

FIG. 11A is a front view of an encapsulated PCD embodiment of the PCDelement of the present invention.

FIG. 11B is a section view of another encapsulated PCD embodiment of thePCD element of the present invention.

FIG. 11C is a section view of still another encapsulated PCD embodimentof the PCD element of the present invention.

FIG. 12A is perspective view of a CVD/PVD applied surface for anotherembodiment of the PCD element of the present invention.

FIG. 12B is an enlarged perspective view of the crystal structure of theembodiment of the PCD element of the present invention shown in FIG.12A.

FIG. 13 is a section view of a wire drawing die having a PCD element ofthe present invention.

FIG. 14 is perspective view of a heat sink having a PCD element of thepresent invention.

FIG. 15 is perspective view of a bearing having a PCD element of thepresent invention.

FIGS. 16A and 16B are front views of the mating parts of a valve havinga PCD element of the present invention.

FIG. 17A is a side view of an indentor having a PCD element of thepresent invention.

FIG. 17B is a partial section view of a punch having a PCD element ofthe present invention.

FIG. 18 is perspective view of a measuring device having a PCD elementof the present invention.

DETAILED DESCRIPTION

The polycrystalline diamond or diamond-like material (PCD) element 2 ofthe present invention is shown in FIG. 1A. The PCD element 2 has aplurality of partially bonded superhard, diamond or diamond-like,crystals 60, (shown in FIGS. 7 and 9) a catalyzing material 64, and aninterstitial matrix 68 formed by the interstices 62 among the crystals60. The element 2 also has one or more working surfaces 4 and thediamond crystals 60 and the interstices 62 form the volume of the body 8of the PCD element 2.

The working surface 4 is any portion of the PCD body 8 which, inoperation, may contact the object to be worked. In this specification,when the working surface 4 is discussed, it is understood that itapplies to any portion of the body 8 which may be exposed and/or used asa working surface. Furthermore, any portion of any of the workingsurface 4 is, in and of itself, a working surface.

During manufacture, under conditions of high-temperature andhigh-pressure, the interstices 62 among the crystals 60 fill with thecatalyzing material 64 just as the bonds among the crystals 60 are beingformed. In a further step of the manufacture, some of the catalyzingmaterial 64 is selectively depleted from some of the interstices 62. Theresult is that a first volume of the body 8 of the PCD element 2 remotefrom the working surface 4 contains the catalyzing material 64, and asecond volume of the body 8 adjacent to the working surface 4 issubstantially free of the catalyzing material 64. The interstices 62which are substantially free of the catalyzing material 64 are indicatedby numeral 66.

Therefore, the interstitial matrix 68 of the body 8 adjacent to at leasta portion of the working surface 4 is substantially free of thecatalyzing material 64, and the remaining interstitial matrix 68contains the catalyzing material 64. The PCD element 2 may be bonded toa substrate 6 of less hard material, usually cemented tungsten carbide,but use of a substrate 6 is not required.

Because the body adjacent to the working surface 4 is substantially freeof the catalyzing material 64, the deleterious effects of thebinder-catalyzing material 64 are substantially decreased, and thermaldegradation of the working surface 4 due to the presence of thecatalyzing material 64 is effectively eliminated. The result is a newPCD element 2 that has the enhanced thermal properties approximatingthat of the so called thermally stable PCD elements, while maintainingthe toughness, convenience of manufacture, and bonding ability of thetraditional PDC elements. This translates to higher wear resistance incutting applications, higher heat transfer capacity in heat sinkapplications, higher load capacity in bearing applications, less surfacedistortion in valve applications, and has advantages in numerous otherapplications including hollow dies, indentors, tool mandrels, and wearelements. Details of specific applications of the new PCD element 2 willbe discussed in more detail later in the specification.

Referring now to the photo-micrograph of a prior art PCD element in FIG.6, and also the microstructural representation of a PCD element of theprior art in FIG. 8, it is well known that there is a randomcrystallographic orientation of the diamond or diamond-like crystals 60as shown by the parallel lines representing the cleavage planes of eachcrystal 60. As can be seen, adjacent crystals 60 have bonded togetherwith interstitial spaces 62 among them. Because the cleavage planes areoriented in different directions on adjacent crystals 60 there isgenerally no straight path for diamond fracture. This structure allowsPCD materials to perform well in extreme loading environments where highimpact loads are common.

In the process of bonding the crystals 60 in a high-temperature,high-pressure press, the interstitial spaces 62 among the crystals 60become filled with a binder-catalyzing material 64. It is thiscatalyzing material 64 that allows the bonds to be formed betweenadjacent diamond crystals 60 at the relatively low pressures andtemperatures present in the press.

The prior art PCD element has at least one continuous matrix of crystals60 bonded to each other with the many interstices 62 containing abinder-catalyzing material 64, typically cobalt or other group VIIIelement. The crystals 60 comprise a first continuous matrix of diamond,and the interstices 62 form a second continuous matrix of interstices 62known as the interstitial matrix 68, containing the binder-catalyzingmaterial. In addition, there are necessarily a relatively few areaswhere the diamond to diamond growth has encapsulated some of thebinder-catalyzing material. These “islands” are not part of thecontinuous interstitial matrix 68 of binder-catalyzing material 64.

Referring now to FIGS. 7 and 9, shown is a cross section of the PCDelement 2 of the present invention. The PCD element 2 may be formed inthe same manner as the prior art PCD elements described above. In apreferred embodiment, after a preliminary cleanup operation or at anytime thereafter in the process of manufacturing, the working surface 4,70, 72 of the PCD element 2 is processed in a manner which removes aportion of the binder-catalyzing material from the adjacent body. Theresult is that the interstices 62 among the diamond crystals 60 adjacentto the working surface are substantially free of the catalyzing material64 indicated by numeral 66. The portion of the working surface 4, 70, 72that is free of the catalyzing material 64 is not subject to the thermaldegradation encountered in the other areas of the PCD, resulting inimproved thermal characteristics.

There are many methods for removing or depleting the catalyzing material64 from the interstices 62. In one method, the catalyzing material 64 iscobalt or other iron group material, and the method of removing thecatalyzing material 64 is to leach it from the interstices 62 near theworking surface 4, 70, 72 of a PCD element 2 in an acid etching processto a depth of greater than about 0.2 mm. It is also possible that themethod of removing the catalyzing material 64 from near the surface maybe by electrical discharge, or other electrical or galvanic process orby evaporation.

In another method for depleting the catalyzing material 64 from theinterstices the catalyzing material 64 is depleted by combining itchemically, such as alloying, with another material such that it nolonger acts as a catalyzing material. In this method, a material mayremain in the interstices among the diamond crystals 60, but thatmaterial no longer acts as a catalyzing material 64 effectively removingit.

In still another method for depleting the catalyzing material 64 fromthe interstices 62, the catalyzing material 64 is removed by causing itto transform into a material that no longer acts as a catalyzingmaterial. This may be accomplished by a crystal structure change, phasechange, mechanical “working”, thermal treatment or other treatmentmethods. This method may apply to non-metallic or non-reactivecatalyzing materials. Again, a material may remain in the interstices 62among the diamond crystals, but that material no longer acts as acatalyzing material 64 effectively removing the catalyzing material.

Once the catalyzing material 64 adjacent to the working surface 4, 70,72 has been rendered ineffective, the PCD element 2 of the presentinvention is no longer susceptible to the type of thermal degradationknown to occur in the prior art PCD elements. As previously described,there are two modes of thermal degradation known to be caused by thecatalyzing material 64. The first mode of thermal degradation begins attemperatures as low as about 400 degrees C and is due to differentialthermal expansion between the catalyzing material 64 in the interstices62 and the crystals 60. Upon sufficient expansion the diamond-to-diamondbonding may be ruptured and cracks and chips may occur.

The second mode of thermal degradation begins at temperatures of about750 degrees C. This mode is caused by the catalyzing ability of thebinder-catalyzing material 64 contacting the crystals 60, and causingthe crystals 60 to graphitize as the temperature nears 750 degrees C. Asthe crystals 60 graphitize, they undergo a huge volume increaseresulting in cracking and dis-bond from the body 4. Even a thickness ofa few microns of the catalyzing material 64 on the surfaces of thediamond crystals 60 can enable this mode of thermal degradation.

It would therefore be appreciated by those skilled in the art that formaximum benefit, the catalyzing material 64 must be removed both fromthe interstices 62 among the diamond crystals 60 and from the surfacesof the diamond crystals 60 as well. If the catalyzing material 64 isremoved from both the surfaces of the diamond crystals 60 and from theinterstices 62 the onset of thermal degradation for the diamond crystals60 in that region would approach 1200 C.

This dual degradation mode, however, provides some unexpected benefits.For example, in many applications it is desirable to engineer the wearrate of the working surface. In the present invention, this may beaccomplished by changing the treatment process such that in areasrequiring maximum wear resistance, the catalyzing material is depletedfrom both the interstices 62 and the surfaces of the diamond crystals60. In areas where less wear resistance is desired, for example in aself sharpening tool, those areas would be treated so as to deplete thecatalyzing material 64 primarily from the interstices 62, but allowingsome, if not all, of the diamond crystals 60 to remain in contact withthe catalyzing material.

It should also be apparent, that it is more difficult to remove thecatalyzing material 64 from the surfaces of the diamond crystals 60 thanfrom the interstices 62. For this reason, depending upon the manner inwhich the catalyzing material is depleted, to be effective in reducingthermal degradation, the depth of depletion of the catalyzing material64 from the working surface 4 may vary depending upon the method usedfor depleting the catalyzing material 64.

In some applications, improvement of the thermal threshold to above 400C but less than 750 C is adequate, and therefore a less intensecatalyzing material 64 depletion process is permissible. As aconsequence, it would be appreciated that there are numerouscombinations of catalyzing material 64 depletion methods which could beapplied to achieve the level of catalyzing material 64 depletionrequired for a specific application.

In this specification, when the term “substantially free” is usedreferring to catalyzing material 64 in the interstices 62, theinterstitial matrix 68, or in a volume of the body 8, it should beunderstood that many, if not all, the surfaces of the adjacent diamondcrystals 60 may still have a coating of the catalyzing material 64.Likewise, when the term “substantially free” is used referring tocatalyzing material 64 on the surfaces of the diamond crystals 60, theremay still be catalyzing material 64 present in the adjacent interstices62.

With the catalyzing material 64 removed or depleted, two majormechanisms for thermal degradation are no longer present., However, ithas been found that the catalyzing material 64 has to be removed at adepth sufficient to allow the bonded crystals 60 to conduct away theheat generated by a thermal event to below the degradation temperatureof the crystals 60 where the catalyzing material 64 is present.

In one set of laboratory tests, heat was input into a PCD element 2configured as a cutting element 10. Since this test was designed as astandard wear test for these cutting elements, it provided a reasonablecomparison of cutting elements 10 with various depths of the catalyzingmaterial 64 removal. In these tests, care was taken to assure thedepletion process removed the catalyzing material 64 from both theinterstices 62 and from the surfaces of the diamond crystals 60. Thetest was designed such that a repeatable input of heat was applied tothe cutting edge of the PCD cutting element 10 for a known period oftime.

Once the test was complete, a wear index was calculated. The higher thewear index, the better the wear resistance. Due to the nature of thetest, it is assumed that an increased wear index number indicatesincreased resistance to thermal of the working surface 70, 72 of thecutting element 10.

As can be seen in curve A in the graph of FIG. 10 there is a dramaticincrease in the wear index result for cutting elements 10 when thecatalyzing material 64 depletion depth approaches 0.1 mm. Therefore, forthe types of heat input common in cutting elements 10, a 0.1 mm depth isthe critical depletion depth from the working surface 4, 70, 72 when thecatalyzing material 64 is removed from both interstices 62 and from thesurfaces of the diamond crystals 60.

In other tests, on cutting elements 10 made with a more economicalprocess for removing the catalyzing material 64, the wear versus depthof depletion is believed to approximate that shown in curve “B” of FIG.10. The catalyzing material 64 depletion process used in these cutterswas not as effective for removing the catalyzing material 64 from thesurfaces of the diamond crystals 60 as the process of curve “A”.Therefore, it was not until most of the catalyzing material 64 wasremoved from the interstices 62 to a depth of about 0.2 mm that the wearrate improved to that of curve “A”.

It is believed that thermal degradation relating to wear rates as shownin curve “C” of FIG. 10 can be engineered into PCD elements 2 where itis beneficial. For example, it may be desirable to have edges of curvedcutting elements 10 remote from the center of contact to wear morequickly than the center point. This would to preserve the curved shapeof the cutting element, rather than having it become a flat surface.

Improved thermal degradation resistance improves wear rates becausediamond is an extremely good thermal conductor. If a friction event atworking surface 4, 70, 72 caused a sudden, extreme heat input, thebonded diamond crystals would conduct the heat in all directions awayfrom the event. This would permit an extremely high temperature gradientthrough the material, possibly 1000 C per mm or higher. A gradient thissteep would enable the working surface 4, 70, 72 to reach 950 C, and notcause significant thermal degradation if interstices 62 and the surfacesof the diamond crystals 62 adjacent to the working surface aresubstantially free of the catalyzing material 64 to a depth of just 0.2mm from the source of the heat.

It should be apparent that the temperature gradient will vary dependingupon the crystal 60 size and the amount of inter-crystal bonding.However, in field tests of cutting elements 10 for earth boring bits,removal of substantially all of the catalyzing material 64 from theinterstices 62 to a distance D of about 0.2 mm to about 0.3 mm from aworking surface 4, 70, 72 produced dramatic improvements in wearresistance, with a combination of a 40% increase in rate of penetrationand a 40% improvement in wear resistance. The improvement in wearresistance indicates that the attrition of the diamond crystals 60 dueto catalyzing material 64 induced thermal degradation was dramaticallyreduced. The rate of penetration increase is believed to be due to theability of the cutter to remain “sharper” longer due to the increasedwear resistance.

There are other possible constructions of PCD elements that benefit fromdepletion or removal of the catalyzing material 64 as described above.As shown in FIGS. 11A, 11B and 11C another embodiment of the presentinvention is a compound PCD element 102. The PCD element 102 has a body108 with a group VIII binder-catalyzing material with a second preformedPCD element 110 embedded within it. The embedded PCD element 110 may beflush with the working surface 104 of the encapsulating PCD element 120as shown in FIG. 11A, or it may be embedded wholly within theencapsulating PCD element 120 as shown in FIG. 11B. This embedded PCDelement 110 is made in a process using powdery carbonates of Mg, Ca, Sr,and Ba as the binder-catalyzing material, and is formed into a compoundPCD element as described in the commonly assigned co-pending U.S. patentapplication Ser. No. 09/390,074 herein incorporated by reference.

In this embodiment, since the embedded preformed PCD element 110 isformed at higher pressures, the diamond density may be made higher thanthat of the encapsulating PCD element 120. In this construction sincethe embedded PCD element 110 has a catalyzing material with a higheractivation temperature, it may for example, be beneficial to deplete thecatalyzing material only in the working surface of the encapsulating PCDelement 120. Furthermore, the embedded PCD element 110 may be positionedwithin the encapsulating PCD element 120 to take advantage of the higherimpact resistance of the embedded PCD element 110 combined with theimproved wear resistance of the encapsulating element 120.

As shown in FIGS. 9, 11A, 11B, and 11C, the element 102 has a pluralityof partially bonded diamond crystals 60, a catalyzing material 64 and abody 108 with a working surface 104. The volume 112 of the body adjacentthe working surface 104 has a substantially higher diamond density thanelsewhere 114 in the body 108, and the volume 112 is substantially freeof the catalyzing material 64.

Several embedded PCD elements 110 may be arranged in the compoundelement 100, as shown in FIG. 11C, in a manner where the best of bothimpact resistance and improved wear resistance may be realized.

It may be desirable to deplete the catalyzing material in the embeddedPCD element 110 as well as the catalyzing material of the encapsulatingPDC element 120. This combination would provide an element with thehighest possible impact strength combined with the highest possible wearresistance available in diamond elements for commercial use.

In FIGS. 12A and 12B another embodiment of the PCD element 202 of thepresent invention is shown. In this embodiment, the PCD element 202 isfirst formed in the manner of the prior art. After a surface has beenprepared, a CVD or PVD process is used to provide a closely packed setof epitaxially oriented crystals of diamond 260 deposited upon a futureworking surface 204 on a portion 210 of the PCD element 202. Theassembly is then subjected to a high-pressure high-temperature processwhereby the deposited diamond crystals 260 form diamond to diamond bondswith each other, and to the diamond crystals in the parent PCD. Thisdiamond-to-diamond bonding is possible due to the presence of thecatalyzing material 64 infusing from the surface of parent PCD element202.

After cleanup, a portion of the working surface 204 is treated todeplete the catalyzing material 64 from the CVD or PVD deposited layer.The final product is a PCD element having one portion of a workingsurface 204 with a volume 214 much higher in diamond density than thatof the other surfaces 280 of the PCD element 202. This region 214 ofhigh diamond density is subsequently depleted of the catalyzing material64. Portions of the other surfaces 280 of the PCD element 202 may bedepleted of the binder catalyzing material as well.

In general the elements 102, 202 shown in FIGS. 11A, 11B, 11C, 12A, and12B may be characterized as PCD element 102, 102 having a body 108, 208with a working surface 104, 204. The diamond density adjacent theworking surface 104, 204 is substantially higher than elsewhere in thebody 108, 208, and is substantially free of the catalyzing material 64.

One particularly useful application for the PCD element 2 of the presentinvention is as cutting elements 10, 50, 52 as shown in FIGS. 1B, 4 and5. The working surface of the PCD cutting elements 10, 50, 52 may be atop working surface 70 and/or a peripheral working surface 72. The PCDcutting element 10 of FIG. 1B is one that may be typically used in fixedcutter type rotary drill bits 12, or for gauge protection in other typesof downhole tools. The PCD cutting element 50 shown in FIG. 5 may beshaped as a dome 39. This type of PCD cutting element 50 has an extendedbase 51 for insertion into sockets in a rolling cutter drill bit 38 orin the body of both types of rotary drill bits, 12, 38 as will bedescribed in detail.

The PCD cutting element 52 of FIG. 4 is adapted for use in a machiningprocess. Although the configuration of the cutting element 52 in FIG. 4is rectangular, it would be appreciated by those skilled in the art thatthis element could be triangular, quadrilateral or many other shapessuitable for machining highly abrasive products are difficult to machinewith conventional tools.

The PCD cutting element 10 may be a preform cutting element 10 of afixed cutter rotary drill bit 12 (as shown in FIG. 2). The bit body 14of the drill bit is formed with a plurality of blades 16 extendinggenerally outwardly away from the central longitudinal axis of rotation18 of the drill bit. Spaced apart side-by-side along the leading face 20of each blade is a plurality of the PCD cutting elements 10 of thepresent invention.

Typically, the PCD cutting element 10 has a body in the form of acircular tablet having a thin front facing table 30 of diamond ordiamond-like (PCD) material, bonded in a high-pressure high-temperaturepress to a substrate 32 of less hard material such as cemented tungstencarbide. The cutting element 10 is preformed and then typically bondedon a generally cylindrical carrier 34 which is also formed from cementedtungsten carbide, or may alternatively be attached directly to theblade. The PCD cutting element 10 has working surfaces 70 and 72.

The cylindrical carrier 34 is received within a correspondingly shapedsocket or recess in the blade 16. The carrier 34 will usually be brazedor shrink fit in the socket. In operation the fixed cutter drill bit 12is rotated and weight is applied. This forces the cutting elements 10into the earth being drilled, effecting a cutting and/or drillingaction.

The PCD cutting elements 10 may also be applied to the gauge region 36of the bit 12 to provide a gauge reaming action as well as protectingthe bit 12 from excessive wear in the gauge region 36. In order to spacethese cutting elements 10 as closely as possible, it may be desirable tocut the elements into shapes, such as the rectangular shape shown, whichmore readily fit into the gauge region 36.

In a second embodiment, the cutting element 50 (as shown in FIG. 5) ofthe present invention is on a rolling cutter type drill bit 38, shown inFIG. 3. A rolling cutter drill bit 38 typically has one or moretruncated rolling cone cutters 40, 41, 42 assembled on a bearing spindleon the leg 44 of the bit body 46. The cutting elements 50 may be mountedas one or more of a plurality of cutting inserts arranged in rows onrolling cutters 40, 41, 42, or alternatively the PCD cutting elements 50may be arranged along the leg 44 of the bit 38. The PCD cutting element50 has a body in the form of a facing table 35 of diamond or diamondlike material bonded to a less hard substrate 37. The facing table 35 inthis embodiment of the present invention is in the form of a domedsurface 39 and has working surfaces 70 and 72. Accordingly, there areoften a number of transitional layers between the facing table 35 andthe substrate 37 to help more evenly distribute the stresses generatedduring fabrication, as is well known to those skilled in the art.

In operation the rolling cutter drill bit 38 is rotated and weight isapplied. This forces the cutting inserts 50 in the rows of the rollingcone cutters 40, 41, 42 into the earth, and as the bit 36 is rotated therolling cutters 40, 41, 42 turn, effecting a drilling action.

In another embodiment, the PCD cutting element 52 of the presentinvention is in the form of a triangular, rectangular or other shapedmaterial for use as a cutting insert in machining operations. In thisembodiment, the cutting element 52 has a body in the form of a facingtable 54 of diamond or diamond like material bonded to a less hardsubstrate 56 with working surfaces 70 and 72. Typically, the cuttingelement 52 would then be cut into a plurality of smaller pieces whichare subsequently attached to an insert 58 that is mounted in the toolholder of a machine tool. The cutting element 52 may be attached to theinsert by brazing, adhesives, welding, or clamping. It is also possibleto finish form the cutting element 52 in the shape of the insert in ahigh-temperature high-pressure manufacturing process.

As shown in FIGS. 13-18, PCD elements 2, 102, 202 of the presentinvention may also be used for other applications such as hollow dies,shown for example as a wire drawing die, 300 of FIG. 13 utilizing a PCDelement 302 of the present invention. It may also be desirable toutilize the excellent heat transfer capabilities of the PCD element 2,102, 202 along with its electrical insulation properties as a heat sink310 with a PCD element 312 of the present invention.

Other applications include friction bearings 320 with a PCD bearingelement 322 shown in FIG. 15 and the mating parts of a valve 340, 344with surfaces 342 having a PCD element 342 of the present invention asshown in FIGS. 16A and 16B. In addition, indentors 360 for scribes,hardness testers, surface roughening, etc. may have PCD elements 362 ofthe present invention as shown in FIG. 17A. Punches 370 may have eitheror both dies 372, 374 made of the PCD material of the present invention,as shown in FIG. 17B. Also, tool mandrels 382 and other types of wearelements for measuring devices 380, shown in FIG. 18 may be made of PCDelements of the present inventions. It should be understood that almostevery application for polycrystalline diamond would benefit from thecatalyzing material depleted PCD elements of the present invention.

Whereas the present invention has been described in particular relationto the drawings attached hereto, it should be understood that other andfurther modifications apart from those shown or suggested herein, may bemade within the scope and spirit of the present invention.

What is claimed is:
 1. A method of manufacture of an earth boring drillbit, the drill bit comprising a bit body and a polycrystalline diamondelement, the polycrystalline diamond element comprising bonded diamondcrystals and a catalyzing material, a working surface on thepolycrystalline diamond element; comprising the steps of treating thepolycrystalline diamond element to render a second volume adjacent tothe working surface thereof substantially free of the catalyzingmaterial to a depth of at least about 0.1 mm from the working surfacewhile permitting the catalyzing material to remain in a first volume ofthe polycrystalline diamond element, and mounting the polycrystallinediamond element on the bit body.
 2. The method of claim 1, wherein thesecond volume is rendered substantially free of catalyzing material byleaching the catalyzing material from the second volume.
 3. The methodof claim 1, wherein the second volume is rendered substantially free ofcatalyzing material by converting the catalyzing material in the secondvolume to a form in which it does not have a catalyzing effect.
 4. Themethod of claim 1, wherein the second volume is rendered substantiallyfree of catalyzing material by reacting the catalyzing material to forma substance which does not have a catalyzing effect.
 5. The method ofclaim 1, wherein the second volume is rendered substantially free ofcatalyzing material by electrical discharge.